/* 外部样式 */
.header{
    height: 100px;
    background-color: #f00;
}
.footer{
    background-color: #aaa;
    height: 250px;
    display: flex;
    justify-content: center;
    align-items: center;
}
.footer div{
    width: 200px;
    height: 200px;
    margin: 0 20px;
}
.box{
    height: 200px;
    background-color: #888;
}
.center{
    margin: 0 auto;
    width: 1200px;
    height: 80px;
    background-color: #ff0;
}